Project Summary This proposal has two aims. The first is to conduct an experiment varying the offer of a housing voucher within the national Section 8 Housing Program and to test how this offer affects the biology and health of adults and young children. This is important because randomized control trials of voucher effects on health have produced conflicting results and also because this experiment affords families the opportunity to use their voucher to increase both the quality of the new neighborhood to which they move and also the disposable income they receive. By contrast, the most successful past study only varied the change in neighborhood quality, albeit to a greater degree than is expected in this study. Thus, we can test the robustness of voucher effects on health across different causal mechanisms as well as different cities, times and study populations. The second and main purpose is to explain why vouchers affect health. We test five different social processes that might be responsible: The quality of the new neighborhood, the additional disposable income a family receives, reduced psychosocial stress, more money to purchase health services, and exposure to more social models of a healthier lifestyle. To test these possible causal mechanisms, we examine families in four cities who apply for a Section 8 housing voucher lottery, half of whom are randomly selected to get one and the other half are not. Then, over three waves of measurement, one at baseline and two at different posttest time points, we assess the vouchers affect (i) each of these possible mediating mechanisms, (ii) adult and child biology using three biomarkers for the adults and at least four for the children, and (iii) various health outcomes linked to the metabolic, immunological and cognitive processes that voucher-induced neighborhood upgrades and voucher-induced increases in disposable income might affect. This would be the first housing voucher experiment designed specifically to examine biology and health in detail, and to do so for both adults and very young children. Since both upgraded neighborhoods and additional disposable income are markers of SES, it also would be the first large-scale natural experiment to test for clear causal links between an exogenous SES shock and biology and health.